More changes in marine weather information

Feb 22, 2018

by Ken McKinley

Last month, I wrote about some changes to the website of NOAA’s Ocean Prediction Center (ocean.weather.gov) and also to some of the products they produce. As noted in that newsletter, the workflow is changing for the meteorologists at the OPC as they develop newer digital products, though those products are difficult to receive at sea because of slow Internet connection speeds or, for some vessels, no Internet availability at all.

There are some additional changes coming regarding surface analysis and forecast charts that will take effect in early March. In this newsletter, I will go through these changes and provide some examples.

First, let’s review which surface charts are available on the OPC website. There are two forecast cycles each day: one that begins with data gathered at 1200 UTC, and another that begins at 0000 UTC. Surface analysis charts are produced on each cycle, and these show isobars and weather features (highs, lows, fronts, etc.) as they existed at the start of the cycle for both the Atlantic and Pacific oceans. In fact, these charts are also produced at 0600 and 1800 UTC each day. The 24-hour regional forecast charts are produced on each cycle for the western Atlantic and eastern Pacific. The 48-hour full ocean forecast charts are also produced on each cycle for each ocean, and the 96-hour full ocean forecast charts are produced only on the 1200 UTC forecast cycle.

In addition to isobars and weather features, each chart also depicts marine warnings (Gale, Storm, Hurricane Force) and indicates areas of heavy freezing spray and the location of ice edges. Also, high and low pressure centers are tracking in 24-hour increments centered on the valid time of the charts, and arrows are placed on the charts indicating the forecast movement of these pressure centers. For analysis charts, the arrows only show the motion of the systems from the valid time of the chart forward, but for forecast charts the tracks are shown for both 24 hours previous to the valid time of the chart and for 24 hours subsequent to the valid time of the chart. The forecast central pressure of the highs and lows are also shown for the forecast positions of the pressure centers. Figure 1 shows a 48-hour surface forecast chart for the Pacific, and Figure 2 shows a 96-hour surface forecast chart for the Atlantic, and all of the features noted above can be seen on these charts.

The changes in these charts will affect only the tracking information (arrows and forecast positions) for highs and lows. Beginning in early March, most tracking information will be removed from the charts. Only lows that are producing (or are expected to produce) warning-category winds will be tracked, and those systems will only be tracked from the valid time of each chart forward 24 hours. This means that tracking information for all highs will no longer be shown on the charts, and lows that are not producing (or expected to produce) at least gale-force winds will also not have tracking information included. In addition, tracking information prior to the valid time on forecast charts for all lows will not be provided. Figure 3 shows the same 48-hour forecast chart for the Pacific as in Figure 1, except with the information blacked out that will no longer appear on the chart starting in March, and Figure 4 does the same for the 96-hour Atlantic forecast chart in Figure 2.

At the same time as these changes are implemented, a new 72-hour surface forecast chart will be added on the 1200 UTC forecast cycle, and a new 72-hour wind/wave chart will be added as well.

For ocean voyagers, this means that following the progress of surface systems through the forecast cycle will require a bit more attention to the charts. It will be necessary to look at all the charts through the forecast cycle carefully to determine how systems are forecast to move, particularly for systems that will have no tracking at all. It may be worth the time to create your own tracking arrows from the information on the charts for the areas where you will be cruising. After all, winds circulating around a well-defined high will certainly impact your voyage plan, as will winds of 30 knots or less around a low. On the other hand, voyagers will have a new chart at the 72-hour forecast time available to show the surface pattern through the entire ocean basin on the 1200 UTC cycle, making charts available for one, two, three and four days ahead on that cycle.

As in the previous newsletter, my advice is to use the remaining months of the Northern Hemisphere cold season to become familiar with the product changes in order to be ready for the 2018 sailing season.